1. Field of the Invention
The present invention relates to improved shift logic for an automated vehicular mechanical transmission system. In particular, the present invention relates to a control method/system having logic rules whereby at least certain upshifts are commanded only at substantially steady-state throttle conditions to minimize the occurrence of unwanted upshifts.
2. Description of the Prior Art
Fully and partially automated vehicular mechanical transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4,850,236; 5,109,721; 5,393,276; 5,409,432 and 5,425,284, the disclosures of which are incorporated herein by reference. Such transmissions having an automatic shift mode typically base shift decisions upon shift point profiles or shift schedules, which often are graphically represented on a graph of throttle position (demand) versus engine, output shaft or vehicle speed. It is known to temporarily modify these shift profiles in view of various sensed vehicle operating conditions to modify vehicle performance, for antihunt purposes or the like. Examples of such shift logic may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802; 4,852,006; 4,916,979; 5,053,963 and 5,406,861, the disclosures of which are incorporated herein by reference.
A problem not addressed by the prior art shift logic involves unwanted upshifting which occasionally occurred if the vehicle operator is rapidly changing throttle demand position.
Present demand-based shift point algorithms use instantaneous demand to determine the shift point speeds. In cases of steady-state or slowly varying demand, this provides logical shifting responses to the driver's demands, the shift point is pushed higher for heavy demand and lower for light demand. However, in the case of demand which is changing relatively quickly, this strategy can create shifts which do not follow with what the driver is trying to do.
If the driver is on the throttle but below the upshift point associated with his particular demand and then comes off the throttle, an upshift can be triggered with the present shift strategy as the demand transitions toward 0%. In this case, the driver may have intended to slow down, but the system upshifted. In another case, if the driver is off the throttle and then gets on it, an upshift can be triggered as demand increases. The driver may have wanted more power, but again, the system upshifted. In both cases, responding to a transitory demand level caused the system to upshift when the situation might have been better handled by remaining in place.
As a note, for setting downshift points, the prior art shift point strategy works logically based upon instantaneous demand. Increasing throttle is more likely to produce a downshift to provide more power, and decreasing throttle is more likely to hold the present gear for better fuel economy.